A variety of mount assemblies are presently available to isolate vehicle vibrations, such as for automobile and truck engines and transmissions. One of the most popular mounts today is the hydraulic-elastomeric mount. Recent improvements in the decoupler mechanism, such as a mount shown in U.S. patent application No. 008,851, filed Jan. 30, 1987 and entitled "Hydraulic-Elastomeric mount Displacement Decoupler", have provided significant improvement in the performance and efficiency of operation.
The hydraulic mount assembly of this prior invention includes a reinforced, hollow rubber body that is closed by a resilient diaphragm so as to form a cavity. This cavity is partitioned by a plate into two chambers that are in fluid communication through a relatively large central orifice in the plate. The first or primary chamber is formed between the orifice plate and the body. The secondary chamber is formed between the plate and the diaphragm.
The decoupler is positioned in the orifice of the plate and reciprocates in response to the vibrations so as to produce small volume changes in the two chambers. When, for example, the decoupler moves toward the diaphragm, the volume of the primary chamber increases and the volume of the secondary chamber decreases. In this way, at certain small vibratory amplitudes and high frequencies, the major fluid flow is through the decoupler and undesirable hydraulic damping is eliminated. In effect, this freely floating decoupler is a passive tuning device.
In addition to the large central orifice, a smaller orifice track is provided, extending around the perimeter of the orifice plate. Each end of the track has one opening: one communicating with the primary chamber and the other to the secondary chamber. The orifice track provides the hydraulic mount assembly with another passive tuning component, and when combined with the freely floating decoupler provides at least three distinct dynamic modes of operation. The operating mode is primarily determined by the flow of the fluid between the two chambers.
More specifically, small amplitude vibrating inputs, such as from the engine or the like, produce no damping due to decoupling, as described above. On the other hand, large amplitude vibrating inputs produce high velocity fluid flow through the orifice track, and accordingly a high level of damping force and smoothing action. As a third (intermediate) operational mode of the mount, medium amplitude inputs produce lower velocity fluid flow through the orifice track resulting in the desired medium level of damping. In each instance, as the decoupler moves from one seated position to the other, a relatively limited amount of fluid can bypass the orifice track by moving around the sides of the decoupler to smooth the transition between the operational modes.
While the three distinct modes of operation provided by present production hydraulic mounts thus provide generally satisfactory operation, they are not sufficient to furnish the desired maximum damping and noise suppression under all the continuously varying conditions encountered during vehicle operation. In response to this need, one approach is to provide a dynamic system that utilizes a pneumatic bladder to engage the diaphram in such a way as to modulate fluid flow into the secondary chamber, as set forth in U.S. patent application No. 929,328, filed Nov. 10, 1986, entitled "Variable Hydraulic-Elastomeric Assembly".
Specifically, an inflatable bladder is mounted externally and in close proximity to the diaphragm, so when inflated, the bladder occupies the area of normal diaphragm expansion. This in effect creates an artificial stiffening of the diaphram, and in turn adds resistance to the movement of the fluid between the chambers. Thus, operation of the hydraulic mount is variable in response to driving conditions by varying the air pressure inside the bladder. The pressure is controlled by a computer in response to transducers mounted on the vehicle. At a maximum bladder inflation, the diaphgragm is forced toward the partition and into positive engagement with the decoupler. In this manner, the decoupler is disabled and forced into a seated position toward the primary chamber, creating a condition of maximum stiffness in the mount.
Another hydraulic mount assembly in the prior art is disclosed in U.S. Pat. No. 4,583,723 to Ozawa. The movement of a two portion plate between the two chambers is controlled by an electromagnetic coil. This system provides either minimum damping by allowing maximum plate movement when the coil is deenergized, or maximum damping by restricting the movement when energized. Hence, the mount operates as an ON/OFF device, without any appreciable intermediate decoupler control. The plate is not allowed to float with a varying degree of restriction, thus substantially limiting the modulation capability.
A need is therefore identified for an improved hydraulic mount assembly that provides for an active or variable control of the dynamic characteristics. The dynamic characteristics of the mount can then be tuned, either manually or automatically, to provide the most effective and efficient damping and noise suppression over the entire range of expected operating conditions. It is desirable that vibration/noise circumstances, and any combination, such as engine lugging, rough road conditions, sudden turning and/or rapid acceleration or deceleration, be controlled in a novel and more efficient manner.